v1.2.0

Lots of small improvements, mostly cleaning up code, bugfixes, build stuff. Here are the most notable changes:

• Smaller app! (84 MB -> 30 MB)
• Bugfix: zooming in with + didn't work on some keyboards (by @mlochen in #18)
• Put resources directory next to the executable (instead of inside the JAR)
• Use shaders.yaml for letting users specify custom pipelines of vertex, geometry and fragment shaders
• Cap "types" to 256, correctly render "types" 65-256 when using palette dependent shader by @jroscoe5 in #12
• Add zoom limit by @karolstawowski in #16

Full Changelog: v1.1.3...v1.2.0